Nothing more you can do. Landline numbers also get recycled too.
Just tell them the previous person with this number didn't pay his bills and his account got closed a year ago and now you have this number.
The collection agency ppl that call me asking for the previous owner were very understanding and never called back. However new agencies will call from time to time if they are unaware or if the guy is still giving out their old number
You could always change your number on self serve. It's free to do on your own